Liquid filled fuse cutout with fluid pressure resistant base member formed of insulating material



Dec.l l., 1970 l E. A. vRABl-:L 3,544,944

LIQUID FILLED F C UT WITH FLUID PRESSURE RESISTANT BASE MEM F ED OF ULATING MATERIAL Filed April 1969 i will@ 28 f vend;

United States Patent O LIQUID FILLED FUSE CUTOUT WITH FLUID PRESSURE RESISTANT BASE MEMBER FORMED OF INSULATING MATERIAL Edward A. Vrabel, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Filed Apr. 24, 1969, Ser. No. 818,907 Int. Cl. H01h 85 02, 85 /54 U.S. Cl. 337-204 6 Claims ABSTRACT OF THE DISCLOSURE A liquid filled, fused circiut interrupter having a component supporting base member characterized by features that enable it to safely withstand high fluid pressures to which it is subjected when gases are generated in the interrupter responsive to a fuse rupturing. A unique feature of the base member is the provision in it of a plurality of mounting recesses that are substantially sealed with a moldable epoxy to prevent the flow of high pressure liquid therein when the interrupter is in operation.

It is common practice in present day oil filled cutouts to mount their operating components and power cable terminations on an insulated base member that is formed of high mechanical and electrical strength organic insulating material. Such a base member is in turn rigidly supported in position on one or more walls of the cutout by a number of conventional bolts or screws inserted through apertures in it and threaded into tapped bores on the cutout walls. It has been found in designing oil filled cutouts that these insulating base members constitute a major limitation of the interrupting rating of the cutout because they are relatively susceptible to damage by high pressure fluids. As is well known in the cutout art, when a fuse fuses in an oil filled cutout it suddenly develops a substantial volume of arc generated gas that in turn causes the oil in the cutout to circulate rapidly, under extremely high pressure, within the oil confining container of the cutout. The velocity at which this oil circulates is a direct function of the volume of the oil confining container and the size of the arc formed by the fuse failure, which, in turn, is a function of the current interrupted by the fuse. Thus, as larger currents are interrupted in a given size cutout, greater hydraulic pressures are exerted on its componentmounting insulated base member. Consequently, such base members are often damaged by hydraulic pressures generated within cutouts when excessively large overcurrents are interrupted. Of course, cutout designers understand that the ability of an insulating base member to withstand hydraulic forces frequently determines the maximum safe current interrupting rating of a cutout. And this long standing awareness by those immediately concerned with such design problems has resulted in the development of very strong and relatively durable insulating base members for cutouts. However, because the insulating base members are formed of organic material that has less inherent mechanical strength than the steel and iron parts used to form cutout housings, it is still relatively common to find that when oil filled cutouts are subjected to overcurrents in excess of their normal rating, the insulating base members therein will be split or otherwise damaged to such an extent that the cutouts must be temporarily removed from service to replace the damaged parts.

It is desirable to keep the size of the insulating base member in a cutout as small as possible consistent with obtaining sufficient mechanical strength to withstand the above noted hydraulic stresses, because cutouts frequently are utilized in underground vaults or in metalclad housings that afiord a limited amount of space. Because of this 3,544,944 Patented Dec. 1, 1970 ICC space factor, in addition to utilizing stronger insulating materials designers have attempted to streamline the base members as much as possible to reduce the high hydraulic pressures to which they are subjected. Still, in order to provide adequate component mounting support means on the base members as well as to provide means for mounting the base members themselves, it is necessary to have a substantial number of surface irregularities on these base members. Thus, it is desirable to find some further means for improving the ability of insulated base members within oil filled cutouts to better withstand the hydraulic pressures to which they are exposed.

It is therefore an object of the present invention t0 provide a liquid filled circuit interrupter of a given size that can be safely rated with a higher current interrupting rating than was heretofore possible.

Another object of the present invention is to provide a liquid filled cutout having an insulating base member mounted therein which is better able to withstand the hydraulic pressures developed in the cutout by fusion of a fuse than was heretofore possible.

A still further object of the invention is to provide a high strength insulating base member for a liquid filled cutout which is characterized by having surface irregularities for mounting it in position within the cutout that are streamlined to reduce hydraulic forces developed on these irregular surfaces.

Still another object of the invention is to provide an inexpensive and efficient mounting means for an insulating base member that reduces the probability of breakage for such member when it is subjected to hydraulic pressures.

In one preferred form of the invention, an oil filled cutout is provided with a high dielectric and mechanical strength insulating base member that is secured to a metal support in the oil confining container of the cutout by a plurality of conventional bolts. The bolts are positioned in a plurality of recesses in the insulating base member and the recesses are then filled with a moldable epoxy material that prevents fluid from developing hydraulic pressures within the recesses when fluid is caused to circulate rapidly within the cutout responsive to a fuse rupturing.

Additional objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a side elevation view, partly in cross section, of an oil filled circuit interrupter having a molded base member that is constructed in accordance with the teachings of the present invention.

FIG. 2 is an end View taken along the plane 2 2 of FIG. 1 showing an enlarged section of the molded base member and cutout container illustrated in FIG. 1 of the drawing. v

FIG. 3 is a sectional view, partly in phantom, showing a side elevation of a portion of the insulated base member and associated support illustrated in FIG. l, in combination with the mounting means for this base member.

Referring now to FIG. l of the drawing there is shown a liquid filled circuit interrupter 1 having an oil confiing container 2 made of drawn steel, and a cast iron cover member 3 that is secured to the container 2 by threads 4 cut, respectively, in these two members. A fluid tight seal is formed by annular gasket 5 which is compressed between lip 3a on cover 3` and the top annular edge of the container 2 when these parts are in their normal assembled position. The container 2 and a part of the volume in cover y3 are filled with a suitable insulating liquid such as oil 6.

The basic operating components of the circuit interrupter 1 comprise a molded epoxy fuse carrier 7 that supports a fuse 8 between a pair of flexible fuse links 9 and 10. These flexible links 9 and 10 are respectively electrically and mechanically connected to a pair of switching contacts, one of which is identified by the numeral 11 and the other of which is not visible in FIG. l of the drawing. As can be seen in FIG. `l, the contact 11 is also mounted on the fuse carrier 7 by a rigid metallic arm member 12 that is supported by a screw 13, the head of which bears against the bottom surface of a cylindrically shaped recess 114 formed in a shoulder portion of fuse carrier 7. It will be understood that in this embodiment of the invention the other contact connected to flexible link is substantially identical in shape, and in its associated mounting means to contact 11. A cooperating pair of contacts, one of which is identified by the numeral 15, are mounted respectively on an insulating base member 16 in a position where they are engaged by the contacts connected to the links 9 and 10` when these contacts are rotated into engagement therewith. Also mounted on the insulating base member 16 are electric power cable terminating means 17 and 18 which anchor the power cables 19 and 20, respectively, in fixed positions within the interrupter 1. As can be seen in FIG. 1, cable -19 is electrically connected to contact by a conductive link 21 and a strap 22 which is coupled by pin 23 to contact 15. A similar electric circuit is completed from cable to the contact electrically connected to flexible link 10. Therefore, when the two pairs of primary contacts 11 and 15 (and the unseen contacts adjacent link 10) are closed, an electric circuit is completed from cable 19 to cable 20 through the operating component parts of interrupter 1, assuming the fuse 8 is in an unruptured condition. Of course, as is intended, when the fuse `8 ruptures, it interrupts the circuit between conductors y19 and 20.

The structural features of the interrupter 1 described thus far are known in the prior art and their particular arrangement and mode of operation are discussed in greater detail in U.S. Pat. 3,132,226, Bennett, issued May 5, 1964 and assigned to the assignee of the present invention. Accordingly, reference can be made to that patent for more detailed information regarding these components if such information is desired. The unique features of the present invention are embodied in the insulating base member 16 and these features will now be described in detail.

The insulating base member 16, in the preferred embodiment of the invention, is formed of a pressed organic insulating material such as a suitable phenolic having glass fibers distributed throughtout its mass so that it forms a high dielectric and mechanical strength member. In order to secure base member 16 in a fixed position with respect to the container .2 and cover 3 of interrupter 1, four cylindrically shaped recesses 24, 25', 26 and 27 (shown in FIG. 2) are formed in the four corners of member 16. Four conventional threaded bolts, such as the bolt 28 shown in FIG. 1, are disposed, respectively, in each of these recesses with the shank portions thereof protruding through smaller preformed apertures, such as the aperture 29 surrounding bolt 28, at one end of each of these recesses 24-27. In the preferred form of the invention illustrated herein these bolts are threaded into tapped apertures on integral supporting arms formed on the cover 3. For example, in FIG. 1 of the drawing, there is shown an integrally cast supporting arm 30 having a tapped threaded aperture 31 therein in which the bolt 28 is threaded when the component parts of the interrupter 1 are in assembled position. These respective component parts are also shown in enlarged detail in FIG. 3 of the drawing. It should be understood that each of the other bolts in recesses 24-27 are similarly mounted to like support means on the cover 3 so that the four corners of base member l16 are firmly fastened to the cover.

In order to prevent the insulating base member 16 from being damaged by high pressure liquid circulating in the container 2 and around cover 3 when the fuse 8 ruptures and causes a substantial volume of gas to be suddenly generated by the resultant electric arc, bodies of moldable epoxy material 32, 33, 34 and 35 are mounted respectively in the recesses 24-27. As can be best seen in FIG. 3 of the drawing, in the preferred form of the invention a glass filler is placed in each recess 24-27 in the manner illustrated with respect to the body of epoxy material 33 which surrounds a piece of glass 36 that serves as a filler to reduce the amount of epoxy required to substantially fill the respective recesses 24-27. It will be understood that other filler materials will afford this same function and such materials may be used in practicing the invention if care is taken to make sure that their respective coefiicients of thermal expansion are close to the related coefficients of the bodies of epoxy material 32-35, and the material of insulating base member 16, so that undue mechanical stresses are not built up within the base member 16.

Because the respective bodies of epoxy material 32-35 are subjected to extremely high fluid pressures when the fuse 8 fails, the inner walls of the recesses 24-27 are roughened, as shown in detail in FIG. 3 of the drawing, in the area of recess 25 identified by the numeral 37. These respective roughened surfaces interlock with the bodies of moldable epoxy material to securely hold them in position within the respective recesses 24-27 under operating conditions that exceed normal ratings for the interrupter. It has been found that by substantially filling the respective recesses 24-27 with the bodies of moldable epoxy material 3235 the current interrupting rating of a given size of circuit interrupter such as interrupter 1 can be increased in excess of 50% without resulting in failure or breakage of the insulating base member 16.

It is believed that this beneficial result is due to the fact that fiuid pressures are kept from building up within the respective mounting recesses 24-25 of insulating base member 16, thus, the forces tending to split or shatter base member 16 are controlled so that they do not exert damaging pressures on these weakened areas of the mounting member 16.

It should be understood that suitably moldable and mechanically strong epoxy must be used to form the bodies of epoxy material 3'2-35. An example of a particular epoxy material suitable for this purpose is an epoxy resin adhesive commercially known as Hysol Corp. 2038. This material can be purchased by brand name from Hysol Corp. without detailed specification. In order to cure Hysol 2038 resin to form the durable bodies of epoxy material 32-35, after these bodies have been formed in recesses 24-27 around the bodies of filler material (36) therein, a curing agent is mixed with it just prior to this forming operation. A suitable curing agent is Hysol Corps Hardener 3475 mixed in a ratio of one part Hardener to four parts adhesive resin.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit interrupter comprising a liquid-confining container partially filled with insulating liquid, a base member composed of high mechanical and electrical strength insulating material, means for rigidly mounting said base member in a predetermined position within said container, at least one electrical contact mounted on said base member, at least one additional contact mounted on a movable insulating member and operable to be engaged with and disengaged from said one contact mounted on the base member, support means for supporting movable insulating member within said container, a fuse mounted in and insulated from said container and electrically connected in series with said contacts, said base member having a pulrality of recesses formed therein through which said means for rigidly mounting said base member are accessible during manufacture of the interrupter, and means for substantially sealing said recesses thereby to prevent liquid from entering and damaging them when liquid is forced to circulate in said container under high pressure in response to said fuse failing.

2. A circuit interrupter as in claim 1 wherein said means for sealing said recesses comprises bodies of a moldable epoxy material disposed respectively in each of said recesses to substantially ll them.

3. A circuit interrupter as in claim 2 including bodies of ller material disposed respectively in each of said recesses and surrounded by said epoxy material.

4. A circuit interrupter as in claim 3 wherein said bodies of filler material comprise pieces of glass having a thermal coeiiicient of expansion substantially equal to that of said epoxy material thereby to reduce the magnitude of mechanical stresses developed between said filler and epoxy materials.

5, A circuit interupter as in claim 2 wherein at least a portion of the inner walls of each of said recesses is roughened to afrord improved mechanical interlocking between said Walls and the respective bodies of epoxy material in juxtaposition therewith.

6. A circuit interrupter as in claim 1 wherein said means for rigidly mounting said base member comprises a plurality of threaded bolts secured in threaded apertures formed in a support positioned in xed relation t0 said container, the head of each of said bolts being positioner respectively in juxtaposition with one end of one of said recesses, each of said recesses being formed to define a cylindrical volume large enough to easily accommodate the head of the bolt therein, and means defining an aperture at said one end of each of said recesses through which the shank portion of the respective bolts in said recesses protrude into said threaded apertures.

References Cited UNITED STATES PATENTS 3,132,226 5/1964 Bennett 337-168X 2,728,120 12/1955 Snyder 52-514X BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner 

